The invention concerns an optical waveguide, in particular for a vehicle, with an optical fiber composed of a polymer material and a protective layer which encloses the fiber.
A problem in vehicle construction is that the increasing use of electronic components in vehicles has led to an intensive growth in conductors which must be connected. In order to reduce the length of the conductors and their total weight and to simplify the design and the fabrication of the wiring harness, bus systems have been developed. They make data transmission between several components over a common conductor possible and thus reduce the required number of conductors.
High rates of transmission can be achieved through bus systems in particular with optical waveguides which work together with optical or electro-optical components. The optical fibers of the optical waveguide include a light-conductive core which is enclosed by a jacket for routing the light as well as possibly one or more outer protective layers. In vehicle construction polymer optical waveguides, for example composed of polymethylmethacrylate (PMMA) and/or fluorinated PMMA, have proven advantageous. Gradient index fibers with a diameter of 1 mm are suitable. In comparison with glass fibers, they offer the advantages of mechanical robustness, ease of handling and fabrication as a result of the large diameter, and the possibility of operation using visible light. The higher degree of damping in comparison to glass, on the other hand, is subordinated in importance in the short transmission paths in vehicles.
It has proven to be a drawback, however, that additional electrical conductors are necessary for the supply of electric power for sensors and actuators. In addition, the optical properties of the common polymer fibers are destroyed or significantly impaired through the absorption of and chemical reaction with substances in their environment. In addition to operating fluids such as lubricants or fuels, the large number of plastic materials used in vehicles which continuously give off substances such as degassing educts or fuels after conclusion of the manufacturing process present a problem. In addition, as a rule, good protection from moisture and thermal stress is required for the fibers, particularly in the case of use in the engine compartment or of linking of sensors or actuators outside of the chassis. Arranging the fibers in a protective sheath or in a plastic tube as is conventional in the state of the art is inadequate for this purpose, since polymers as a rule are not sufficiently gas-tight.
It is also known to provide metal pipes with a corrugation to improve their flexibility and transverse pressure stability as components of electrical cables. The corrugation is at an angle to the longitudinal axis of the pipe. Both spiral corrugations with crests oriented at an acute angle to the longitudinal axis of the pipe as well as corrugations of closed rings oriented at right angles to the axis are common. Through variation of the depth of the corrugations and the distance between them, the mechanical properties of the pipe such as flexibility can be set within broad limits.